1. Field of the Invention
This invention relates generally to propeller propulsion systems for watercraft and more particularly to thrust enhancing devices and apparatus for improving the efficiency of such propeller propulsion means.
2. Description of Related Art
The use of a multi-bladed propeller to propel a watercraft, boat or vessel through the water is ancient. Although other propulsion means have been developed in recent times, the twisted blade propeller remains the mainstay of water propulsion. Although propeller configuration and design have become extremely sophisticated through the use of computerized design techniques, nonetheless as a propeller rotates in water to produce a net axial flow of water which propels the watercraft in the opposite direction thereto, some of the water discharging as prop wash from the propeller does so from the tips at an acute angle of up to 90° to the axial flow or longitudinal axis of the propeller. This nonaxial water flow off the tips of the propeller leads to considerable loss in efficiency and thrust for which the propeller is capable of producing. Moreover, a spiral twist is introduced into the water flow by the propeller which also dissipates or reduces some of the axial thrust potential of the propeller.
A number of prior art devices have attempted to improve the efficiency of water flow produced by propulsion means including these conventional propellers as follows:
U.S. Pat. No. 2,803,211 to Erlbacher
U.S. Pat. No. 3,249,083 to Irgens
U.S. Pat. No. 3,528,382 to Clark
U.S. Pat. No. 3,722,454 to Silvester
U.S. Pat. No. 3,934,538 to Canazzi
U.S. Pat. No. 4,046,097 to Hornung
U.S. Pat. No. 4,505,684 to Holden, et al.
U.S. Pat. No. 4,637,801 to Schultz
U.S. Pat. No. 5,651,707 to Lemont
U.S. Pat. No. 5,906,522 to Hooper
In particular, U.S. Pat. No. 3,528,382 invented by Clark, et al. discloses a propulsive system which will utilize a considerable amount of energy from the rotation of the screw race by restoring it as for and aft propulsive effort on the vessel. A propeller duct assembly for watercraft which enhances the thrust of the propeller is taught by Schultz in U.S. Pat. No. 4,637,801.
U.S. Pat. No. 5,906,522 invented by Hooper discloses a thrust enhancer for a marine propeller. Irgens, in U.S. Pat. No. 3,249,083 teaches marine propulsion units including reaction jet arrangements for developing thrust.
A driving mechanism for watercraft which utilizes the propeller wash to impart additional driving thrust to the vessel is taught by Masta in U.S. Pat. No. 2,884,890 and Lemont teaches a propulsive thrust ring system in U.S. Pat. No. 5,651,707.
U.S. Pat. No. 3,722,454 to Silvester discloses a thrust augmenter device and Holden, et al. discloses a thrust tube propulsion system in U.S. Pat. No. 4,505,684.
The present invention provides an economical easily attachable addition to virtually any watercraft which is propeller driven. The apparatus forces virtually all of the water discharging from the propeller into an axial flow which discharges there from to produce propulsion for the watercraft in a substantially rearwardly axial flow without substantial amounts of radial or spiral twist prop wash energy loss.